/**
 * Copyright (C) 2002-2015   The FreeCol Team
 * <p>
 * This file is part of FreeCol.
 * <p>
 * FreeCol is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 * <p>
 * FreeCol is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * <p>
 * You should have received a copy of the GNU General Public License
 * along with FreeCol.  If not, see <http://www.gnu.org/licenses/>.
 */

package net.sf.freecol.server.ai.mission;

import java.util.logging.Logger;

import javax.xml.stream.XMLStreamException;

import net.sf.freecol.common.io.FreeColXMLReader;
import net.sf.freecol.common.io.FreeColXMLWriter;
import net.sf.freecol.common.model.Ability;
import net.sf.freecol.common.model.Colony;
import net.sf.freecol.common.model.CombatModel;
import net.sf.freecol.common.model.Europe;
import net.sf.freecol.common.model.Location;
import net.sf.freecol.common.model.Direction;
import net.sf.freecol.common.model.PathNode;
import net.sf.freecol.common.model.Player;
import net.sf.freecol.common.model.Settlement;
import net.sf.freecol.common.model.Tile;
import net.sf.freecol.common.model.Unit;
import net.sf.freecol.common.model.pathfinding.CostDeciders;
import net.sf.freecol.common.model.pathfinding.GoalDecider;
import net.sf.freecol.common.util.LogBuilder;
import net.sf.freecol.server.ai.AIMain;
import net.sf.freecol.server.ai.AIMessage;
import net.sf.freecol.server.ai.AIUnit;


/**
 * A mission for a Privateer unit.
 */
public class PrivateerMission extends Mission
{

    private static final Logger logger = Logger.getLogger( PrivateerMission.class.getName( ) );

    /** The tag for this mission. */
    private static final String tag = "AI privateer";

    /**
     * The target for this mission.
     * - A port location to drop off plunder
     * - A unit to attack
     * - An unexplored tile
     */
    private Location target;


    /**
     * Creates a mission for the given <code>AIUnit</code>.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param target The target <code>Location</code> for this mission.
     */
    public PrivateerMission( AIMain aiMain, AIUnit aiUnit, Location target )
    {
        super( aiMain, aiUnit, target );
    }

    /**
     * Creates a new <code>UnitWanderHostileMission</code> and reads
     * the given element.
     *
     * @param aiMain The main AI-object.
     * @param aiUnit The <code>AIUnit</code> this mission is created for.
     * @param xr The input stream containing the XML.
     * @throws XMLStreamException if a problem was encountered
     *      during parsing.
     * @see net.sf.freecol.server.ai.AIObject#readFromXML
     */
    public PrivateerMission( AIMain aiMain, AIUnit aiUnit,
                             FreeColXMLReader xr ) throws XMLStreamException
    {
        super( aiMain, aiUnit );

        readFromXML( xr );
    }


    /**
     * Hack to help REF planning.
     *
     * This should go away.  AI units should not exploit seeing the whole map.
     *
     * @return The distance to the target, or a large value on failure.
     */
    public int getDistanceToTarget( )
    {
        return ( target == null || target.getTile( ) == null
                || ! getUnit( ).hasTile( ) ) ? 1000000
                : getUnit( ).getTile( ).getDistanceTo( target.getTile( ) );
    }

    /**
     * Extract a valid target for this mission from a path.
     *
     * @param aiUnit A <code>AIUnit</code> to perform the mission.
     * @param path A <code>PathNode</code> to extract a target from,
     *     (uses the unit location if null).
     * @return A target for this mission, or null if none found.
     */
    public static Location extractTarget( AIUnit aiUnit, PathNode path )
    {
        if ( path == null ) return null;
        final Unit unit = aiUnit.getUnit( );
        final Player owner = unit.getOwner( );
        final Location loc = path.getLastNode( ).getLocation( );
        Settlement settlement = loc.getSettlement( );
        Tile tile = loc.getTile( );
        Unit other = ( tile == null ) ? null : tile.getDefendingUnit( unit );
        return ( loc instanceof Europe ) ? loc
                : ( other != null
                && invalidUnitReason( aiUnit, other ) == null ) ? other
                : ( settlement != null
                && invalidTargetReason( settlement, owner ) == null ) ? settlement
                : null;
    }

    /**
     * Score a potential attack on a unit.
     *
     * @param aiUnit The <code>AIUnit</code> that may attack.
     * @param defender The <code>Unit</code> to attack.
     * @return A score for the attack.
     */
    private static int scoreUnit( AIUnit aiUnit, Unit defender )
    {
        final Unit attacker = aiUnit.getUnit( );
        int value = 100;
        // Pirates want cargo
        value += defender.getVisibleGoodsCount( ) * 200;
        // But they are wary of danger
        if ( defender.isOffensiveUnit( ) )
        {
            CombatModel.CombatOdds co = attacker.getGame( ).getCombatModel( )
                    .calculateCombatOdds( attacker, defender );
            if ( co != null ) value += ( co.win - 0.5 ) * 200;
        }
        return value;
    }

    /**
     * Evaluate a potential mission for a given unit and path.
     *
     * @param aiUnit The <code>AIUnit</code> to do the mission.
     * @param path A <code>PathNode</code> to take to the target.
     * @return A score for the proposed mission.
     */
    public static int scorePath( AIUnit aiUnit, PathNode path )
    {
        Location loc = extractTarget( aiUnit, path );
        if ( loc instanceof Europe || loc instanceof Colony )
        {
            return 1000 / ( path.getTotalTurns( ) + 1 );
        }
        else if ( loc instanceof Unit )
        {
            return scoreUnit( aiUnit, ( Unit ) loc ) / ( path.getTotalTurns( ) + 1 );
        }
        else if ( loc instanceof Tile )
        {
            return 50 / ( path.getTotalTurns( ) + 1 );
        }
        else
        {
            return Integer.MIN_VALUE;
        }
    }

    /**
     * Gets a <code>GoalDecider</code> for this mission.
     *
     * @param aiUnit The <code>AIUnit</code> that is searching.
     * @param deferOK Enable colony fallback (not implemented).
     * @return A suitable <code>GoalDecider</code>.
     */
    private static GoalDecider getGoalDecider( final AIUnit aiUnit,
                                               boolean deferOK )
    {
        return new GoalDecider( )
        {
            private PathNode bestPath = null;
            private int bestValue = Integer.MIN_VALUE;

            @Override
            public PathNode getGoal( ) { return bestPath; }

            @Override
            public boolean hasSubGoals( ) { return true; }

            @Override
            public boolean check( Unit u, PathNode path )
            {
                int value = scorePath( aiUnit, path );
                if ( bestValue < value )
                {
                    bestValue = value;
                    bestPath = path;
                    return true;
                }
                return false;
            }
        };
    }

    /**
     * Finds a suitable privateering target for the supplied unit.
     *
     * @param aiUnit The <code>AIUnit</code> to find a path for.
     * @param range The maximum number of turns to seek for a target.
     * @param deferOK Not implemented in this mission.
     * @return A path to the new target.
     */
    public static PathNode findTargetPath( AIUnit aiUnit, int range,
                                           boolean deferOK )
    {
        if ( invalidAIUnitReason( aiUnit ) != null ) return null;
        final Unit unit = aiUnit.getUnit( );
        final Location start = unit.getPathStartLocation( );

        // Can the privateer legally reach a valid target from where
        // it currently is?
        return unit.search( start, getGoalDecider( aiUnit, deferOK ),
                            CostDeciders.avoidIllegal( ), range, null );
    }

    /**
     * Finds a suitable privateering target for the supplied unit.
     *
     * @param aiUnit The <code>AIUnit</code> to find a path for.
     * @param range The maximum number of turns to seek for a target.
     * @param deferOK Enables deferring to a fallback colony.
     * @return A <code>PathNode</code> to the target, or null if none found.
     */
    public static Location findTarget( AIUnit aiUnit, int range,
                                       boolean deferOK )
    {
        PathNode path = findTargetPath( aiUnit, range, deferOK );
        return ( path != null ) ? extractTarget( aiUnit, path )
                : null;
    }

    /**
     * Why would a PrivateeringMission be invalid with the given unit.
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @return A reason why the mission would be invalid with the unit,
     *     or null if none found.
     */
    private static String invalidMissionReason( AIUnit aiUnit )
    {
        String reason = invalidAIUnitReason( aiUnit );
        if ( reason != null ) return reason;
        final Unit unit = aiUnit.getUnit( );
        return ( ! unit.isCarrier( ) ) ? "unit-not-a-carrier"
                : ( ! unit.isOffensiveUnit( ) ) ? Mission.UNITNOTOFFENSIVE
                : ( ! unit.isEmpty( )
                || ! unit.getCompactGoods( ).isEmpty( ) ) ? "unit-has-cargo"
                : null;
    }

    /**
     * Is this a valid target because it is one of our colonies.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @param settlement The <code>Settlement</code> to test.
     * @return A reason why the mission would be invalid, or null if
     *     none found.
     */
    private static String invalidSettlementReason( AIUnit aiUnit,
                                                   Settlement settlement )
    {
        return ( settlement instanceof Colony )
                ? invalidTargetReason( settlement, aiUnit.getUnit( ).getOwner( ) )
                : Mission.TARGETINVALID;
    }

    /**
     * Is this a valid target because it is a hostile unit.
     *
     * @param aiUnit The <code>AIUnit</code> to test.
     * @param unit The <code>Unit</code> to test.
     * @return A reason why the mission would be invalid, or null if
     *     none found.
     */
    private static String invalidUnitReason( AIUnit aiUnit, Unit unit )
    {
        final Player player = aiUnit.getUnit( ).getOwner( );
        final boolean pirate = aiUnit.getUnit( ).hasAbility( Ability.PIRACY );
        String reason;
        return ( unit == null )
                ? Mission.TARGETINVALID
                : ( ! unit.isNaval( ) )
                ? "privateer-ignores-land-unit"
                : ( player.owns( unit ) )
                ? Mission.TARGETOWNERSHIP
                : ( ( reason = invalidAttackReason( aiUnit, unit.getOwner( ) ) ) != null )
                ? reason
                : ( scoreUnit( aiUnit, unit ) <= 0 )
                ? "privateer-avoids-trouble"
                : null;
    }

    /**
     * Why would this mission be invalid with the given AI unit?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @return A reason for mission invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit )
    {
        return invalidMissionReason( aiUnit );
    }

    /**
     * Why would this mission be invalid with the given AI unit?
     *
     * @param aiUnit The <code>AIUnit</code> to check.
     * @param loc The <code>Location</code> to check.
     * @return A reason for mission invalidity, or null if none found.
     */
    public static String invalidReason( AIUnit aiUnit, Location loc )
    {
        final Player owner = aiUnit.getUnit( ).getOwner( );
        String reason = invalidMissionReason( aiUnit );
        return ( reason != null )
                ? reason
                : ( aiUnit.getUnit( ).isInEurope( ) )
                ? null
                : ( loc == null )
                ? null
                : ( loc instanceof Europe )
                ? invalidTargetReason( loc, owner )
                : ( loc instanceof Settlement )
                ? invalidSettlementReason( aiUnit, ( Settlement ) loc )
                : ( loc instanceof Unit )
                ? invalidUnitReason( aiUnit, ( Unit ) loc )
                : ( loc instanceof Tile )
                ? ( ( ( ( Tile ) loc ).isExploredBy( owner ) ) ? "tile-is-explored"
                : null )
                : Mission.TARGETINVALID;
    }


    // Implement Mission
    //   Inherit dispose, getBaseTransportPriority, isOneTime

    /**
     * {@inheritDoc}
     */
    @Override
    public Location getTransportDestination( )
    {
        return null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location getTarget( )
    {
        return target;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void setTarget( Location target )
    {
        if ( target == null
                || target instanceof Colony || target instanceof Europe
                || target instanceof Unit )
        {
            this.target = target;
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Location findTarget( )
    {
        return findTarget( getAIUnit( ), 8, true );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String invalidReason( )
    {
        return invalidReason( getAIUnit( ), getTarget( ) );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public Mission doMission( LogBuilder lb )
    {
        lb.add( tag );
        final AIUnit aiUnit = getAIUnit( );
        if ( aiUnit.hasCargo( ) )
        { // Deliver the goods
            Mission m = getEuropeanAIPlayer( ).getTransportMission( aiUnit );
            return lbDone( lb, m != null, " transporting" );
        }

        String reason = invalidReason( );
        if ( isTargetReason( reason ) )
        {
            return retargetMission( reason, lb );
        }
        else if ( reason != null )
        {
            return lbFail( lb, false, reason );
        }

        final Unit unit = getUnit( );
        if ( unit.isInEurope( ) )
        {
            Settlement settlement = getBestSettlement( unit.getOwner( ) );
            Tile tile = ( settlement != null ) ? settlement.getTile( )
                    : unit.getFullEntryLocation( );
            unit.setDestination( tile );
            aiUnit.moveToAmerica( );
        }
        if ( unit.isAtSea( ) ) return lbAt( lb );

        Location newTarget = findTarget( aiUnit, 1, true );
        if ( newTarget == null )
        {
            moveRandomlyTurn( tag );
            return lbAt( lb );
        }

        setTarget( newTarget );
        Unit.MoveType mt = travelToTarget( newTarget, null, lb );
        switch ( mt )
        {
            case MOVE: // Arrived at intermediate safe location
                break;

            case MOVE_HIGH_SEAS:
            case MOVE_NO_MOVES:
            case MOVE_NO_REPAIR:
            case MOVE_ILLEGAL:
                return lbWait( lb );

            case MOVE_NO_TILE: // Can happen when another unit blocks a river
                moveRandomly( tag, null );
                return lbDodge( lb );

            case ATTACK_UNIT: // Arrived
                Direction direction = unit.getTile( )
                        .getDirection( getTarget( ).getTile( ) );
                if ( direction != null )
                {
                    AIMessage.askAttack( aiUnit, direction );
                    lbAttack( lb, getTarget( ) );
                }
                else
                { // Found something else in the way!
                    Location blocker = resolveBlockage( aiUnit, getTarget( ) );
                    if ( blocker instanceof Unit
                            && scoreUnit( aiUnit, ( Unit ) blocker ) > 0 )
                    {
                        AIMessage.askAttack( aiUnit,
                                             unit.getTile( ).getDirection( blocker.getTile( ) ) );
                        lbAttack( lb, blocker );
                    }
                    else
                    { // Might be dangerous, try to confuse them:-)
                        moveRandomlyTurn( tag );
                        lb.add( " avoiding ", blocker, "." );
                    }
                }
                return this;

            case MOVE_NO_ACCESS_EMBARK:
            default:
                return lbMove( lb, mt );
        }

        return lbAt( lb );
    }


    // Serialization

    private static final String TARGET_TAG = "target";


    /**
     * {@inheritDoc}
     */
    @Override
    protected void writeAttributes( FreeColXMLWriter xw ) throws XMLStreamException
    {
        super.writeAttributes( xw );

        if ( target != null )
        {
            xw.writeAttribute( TARGET_TAG, target.getId( ) );
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void readAttributes( FreeColXMLReader xr ) throws XMLStreamException
    {
        super.readAttributes( xr );

        target = xr.getLocationAttribute( getGame( ), TARGET_TAG, false );
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String getXMLTagName( ) { return getXMLElementTagName( ); }

    /**
     * Gets the tag name of the root element representing this object.
     *
     * @return "privateerMission"
     */
    public static String getXMLElementTagName( )
    {
        return "privateerMission";
    }
}
